Calibration and quality control of a nuclear-medicine (N-M) radio imaging system

Abstract

Methods for calibrating a Nuclear-Medicine (N-M) imaging system including calibrating an N-M imaging system scanning unit for scanning detector uniformity map and energy resolution as well as generating an angular orientation map of a plurality of scanning units and a line source of radiation. There is further disclosed a jig for holding a line source during a calibration process of an N-M imaging system.

What is claimed is: 
     
       1. A method for calibrating a scanning unit in a nuclear medicine (N-M) imaging system, said method comprising:
 a. providing a scanning unit which is pivotable at a mounting location about a center of rotation (COR), said scanning unit including at least one array of detector modules; 
 b. positioning at least one radiation source at a predetermined distance from said scanning unit and at a predetermined orientation relative to said scanning unit; 
 c. positioning said scanning unit at predetermined initializing position in which said at least one array of detector modules are at an initial pivot angle with respect to said mounting location, wherein at said initial pivot angle said at least one array of detector modules is spatially positioned to have no exposure to radiation effluence (zero S PMT ) from said at least one radiation source; 
 d. sampling pixel exposure of said at least one array of detector modules to measure a first level of said radiation effluence when said at least one array of detector modules is at said initializing position; 
 e. recording said predetermined initializing position of said scanning unit and said measured first level of exposure of said at least one array of detector modules to said radiation effluence when said at least one array of detector modules is at said initializing position; 
 f. rotating said scanning unit about said COR to a second predetermined position, in which said at least one array of detector modules is at a second pivot angle with respect to the mounting location; 
 g. sampling pixel exposure of said at least one array of detector modules to measure a second level of said radiation effluence when said at least one array of detector modules is at said second position; 
 h. recording said predetermined second position of said scanning unit and said measured second level of exposure of said at least one array of detector modules to said radiation effluence when said at least one array of detector modules is at said second position; 
 i. repeating said rotating (f) of said scanning unit to a new predetermined position, different from any previous predetermined position at which said sampling pixel exposure [action (g)] was performed, until radiation effluence signals have been sampled from every module pixel at said predetermined pivot angles; 
 j. generating, for said scanning unit, one or more of a uniformity map, a uniformity correction matrix and a calibration lookup table of photon count from said first and second levels of exposure of said at least one array of detector modules to said radiation effluence when said at least one array of detector modules is at said predetermined positions (c, f, and i); and 
 k. calibrating said detector array of said scanning unit by correcting a registration signal for each of said pixels of each said detector array in accordance with said one or more of a uniformity map, a uniformity correction matrix and a calibration lookup table of photon count. 
 
     
     
       2. The method of  claim 1 , wherein said at least one radiation source includes at least one line radiation source. 
     
     
       3. The method of  claim 2 , wherein in said predetermined orientation a single line radiation source of said at least one line radiation source is positioned in parallel to said COR. 
     
     
       4. The method of  claim 1 , wherein in said predetermined orientation said at least one array of detector modules is oriented in parallel to said radiation effluence. 
     
     
       5. The method of  claim 1 , wherein said calibrating said detector array {action (k)] includes calibrating all said detector modules of said array of said scanning unit at once. 
     
     
       6. The method of  claim 1 , wherein said N-M imaging system includes an encoder configured to measure movement of said scanning unit and wherein said recording (e and h) includes receiving and recording said encoder data. 
     
     
       7. The method of  claim 1 , wherein said rotating said scanning unit [action (f)] includes rotating said scanning unit in a stepwise manner in accordance with predetermined increments. 
     
     
       8. The method of  claim 7 , wherein said predetermined increments are single degree increments. 
     
     
       9. The method of  claim 1 , wherein said scanning unit is configured to rotating in at least one of a clockwise direction and a counterclockwise direction. 
     
     
       10. The method of  claim 9 , and wherein said rotating [action (f)] includes rotating said scanning unit in one of a swiping reciprocating motion and an oscillatory motion. 
     
     
       11. The method of  claim 1  wherein, after said repeating, each said pixel has been exposed to a same dose of radiation. 
     
     
       12. The method of  claim 1 , wherein said correcting includes correcting a registration signal for each said pixel by a multiplicative factor for deviations from said one or more of a uniformity map, a uniformity correction matrix and a calibration lookup table. 
     
     
       13. The method of  claim 1 , wherein said N-M imaging system comprises a gantry rotatable about a gantry COR, a plurality of said scanning units mounted to said gantry. 
     
     
       14. The method of  claim 13 , wherein N-M imaging system includes a plurality of arms configured to extend toward and away from said gantry COR, wherein each of said plurality of scanning units is mounted to said gantry by a respective arm of said plurality of arms. 
     
     
       15. The method according to  claim 1 , wherein said recording (e and h) each comprises receiving and recording encoder data. 
     
     
       16. The method according to  claim 1 , wherein each said detector array is arranged along at least one surface of said scanning unit. 
     
     
       17. The method according to  claim 1 , wherein said sampling pixel exposure of said at least one array of detector modules to said emitted radiation (d and g) includes measuring pixel signals from said detector array. 
     
     
       18. The method according to  claim 1 , wherein said scanning unit is configured to pivot about a longitudinal axis. 
     
     
       19. The method according to  claim 1 , further including generating information regarding detector performance. 
     
     
       20. The method according to  claim 19 , wherein said detector performance includes energy resolution. 
     
     
       21. The method according to  claim 1 , wherein said scanning unit is moveable in at least two dimensions. 
     
     
       22. The method according to  claim 21 , wherein said at least two dimensions include at least one rotational direction and at least one translational direction. 
     
     
       23. The method according to  claim 1 , wherein said at least one source emits isotropic radiation. 
     
     
       24. The method according to  claim 1 , wherein said at least one array of detector modules comprises Cadmium Zinc Telluride (CZT) detectors.